1. Field
One embodiment of the invention relates to, for example, a magnetic disk drive that refreshes data written to a disk, and also relates to a data refreshment method applied to a magnetic disk drive.
2. Description of the Related Art
In recent years, efforts have been made to increase the storage capacity per surface (recording surface) of a disk (magnetic disk) mounted in a magnetic disk drive. To increase the storage capacity per disk surface (that is, the areal density), a linear recording density and/or a track density may be increased. To increase the linear recording density, the number of sectors per track may be increased. To increase the track density, that is, to provide more tracks in the disk surface, the track width may be reduced to decrease a distance between adjacent tracks (that is, a track pitch).
Here, it is assumed that the track pitch is reduced to increase the track density. In general, the shorter the track pitch is, the more markedly a data write to a certain track by a head (magnetic head) degrades the data in a track located adjacent to the certain track. Each track has the same width as that of the head (a write element contained in the head). However, the width of distribution of write magnetic fields generated by the head during the data write is not always equal to the width of the head. The write magnetic fields are applied (leak to) to the periphery of the head. Thus, an excessive reduction in track pitch increases, during a data write to a certain tack on the disk by the head, the level of the adverse effect of leakage fields from the head on a track located adjacent to the certain track.
However, even with the reduction of the track pitch, if the level of the reduction is small, the data in the adjacent track is prevented from being immediately corrupted by one or several data write operations. That is, in general, repeated data write operations gradually degrade the data in the adjacent track depending on the number of operations performed.
Thus, data refreshment (rewrite) is becoming essential for recent magnetic disk drives; the data refreshment is performed to recover the data in the adjacent track degraded by the data write operations. For example, Jpn. Pat. Appln. KOKAI Publication No. 2004-273060 discloses a technique (prior art) of refreshing the data in a track located adjacent to a track for which the number of data writes has reached a predetermined value.
According to the prior art, data is read from the track (adjacent track) located adjacent to the track for which the number of data writes has reached the predetermined value. The read data is temporarily stored in a RAM. The data temporarily stored in the RAM, that is, the data in the adjacent track, is written to the adjacent track again. That is, the data in the track to be subjected to data refreshment is rewritten with the data read from that track. Such a data rewrite process, that is, a data refreshment process, recovers the degraded data. Thus, application of the data refreshment process enables a reduction in track pitch.
However, with the prior art, when a power supply to the magnetic disk drive is interrupted during the data refreshment process, the data to be refreshed may be lost. More specifically, when the power supply to the magnetic disk drive is interrupted during an operation (data write operation) of writing data read from the track (hereinafter referred to as the target track) to be subjected to the data refreshment, to the track again, the data may be lost. The reason for this will be explained below.
First, it is assumed that the power supply is interrupted during the operation of writing data to the target track again. In this case, the operation of writing the data to the target track fails to be completed. Thus, the data in the target track is corrupted. At this time, the data in the target track temporarily stored in the RAM is lost. Thus, even when the power supply is restored, the uncompleted data write operation cannot be performed again. Consequently, the data in the target track is lost.
To prevent such a problem, a particular track on the disk may be used in place of the RAM, described above. That is, the particular track on the disk may be used as a track for temporary saving to which the data in the target track is temporarily saved. In this case, the data read from the target track is written (temporarily saved) to the particular track on the disk. Then, the read data is written to the target track (that is, the track in which the data was present) again. Even if the power supply is interrupted during the rewrite of the data to the target track, the data written (saved) to the particular track is prevented from being lost. Thus, using the data written to the particular track allows the uncompleted data write operation to be performed again.
However, such a write operation as described below is required to refresh the data in the target track using the particular track on the disk in place of the RAM. That is, a write operation is required which allows the data read from the target track to be written (temporarily saved) to the particular track before being written again to the target track. The write operation requires a longer time than a data write to the RAM. The efficiency of the data refreshment process is thus reduced. Two seek operations are also required, one of which moves the head from the target track to the particular track and another which moves the head from the particular track to the target track. The two seek operations further reduce the efficiency of the data refreshment process.
As described above, by using the particular track (track for temporary saving) on the disk in place of the RAM, the interruption of the power supply can be dealt with, but the efficiency of the data refreshment process may decrease.